This invention relates to a solar cell module which includes a series of connected solar cells, each using an amorphous semiconductor film as a photovoltaic cell.
Since amorphous silicon (referred to as a-Si), produced by glow discharge decomposition of a silane gas, is formed by vapor phase growth techniques to facilitate deposition in large areas, it has been expected to be useful as a material for low cost solar cells. In order to efficiently take electric power generated from solar cells, it may be preferable that a structure of a solar cell module is, for example, a configuration as shown in FIG. 2, and that unit cells are connected in series with one another. Transparent electrodes 21,22,23,24 . . . are deposited on a transparent insulating substrate 1, such as glass substrate and the like, so as to obtain a strip-shaped structure. They are produced by depositing ITO (indium tin oxide) or SnO.sub.2 (tin oxide) on an entire surface of the glass substrate 1 by means of electron beam, sputtering, or thermal CVD techniques, and patterning the thus deposited ITO or SnO.sub.2 layer by laser patterning techniques.
A-Si layers 31,32,33,34 . . . and metal electrode layers 41,42,43,44 . . . are provided in the same manner as described above. In this case, for electrically connecting transparent electrode layers to metal electrode layers, respective patterns of the transparent electrodes and the a-Si layers and the metal electrodes are slightly shifted to the left, in relation to the transparent electrodes 21-24, as shown in FIG. 2, whereby transparent electrodes 21,22,23 . . . are connected to metal electrodes 42,43,44 . . . , respectively. The a-Si layer 31,32 . . . has a laminated structure which includes, for example, a p-type layer with a thickness of 100 .ANG., a non-doped layer with a thickness of 0.5 .mu.m, and an n-type layer with a thickness of 500 .ANG. from the side near the transparent electrode.
However, when laser patterning is carried out, there remains a problem to improve the pattern accuracy. The following problems also arise:
(1) automation is difficult because of use of a batch-type process;
(2) the manufacturing cost is increased with increase of the area, since masks are employed;
(3) since three mask alignment processes are necessary, margins for the position alignment are required and the ineffective area against optical regeneration is increased; and
(4) since transparent electrodes are reduced by hydrogen that is generated when patterning of the metal electrode layer is performed by etching using acids, such as phosphoric acids, nitric acids and the like, thereby decreasing the conductivity, the transparent electrode layer must be thicker than usual.
FIG. 3 shows an example of the patterning. That is, an a-Si layer 3 is deposited on the entire outer surface of patterned transparent electrodes 21,22,23,24 et seq. When the a-Si layer is patterned, its portions 51,52,53,54 . . . are evaporated by applying a laser beam thereto. However, since the lower layer of each portion to be evaporated has a thickness which is stepped, the film thickness of the a-Si layer is not always held constant. Therefore, it is very difficult to find conditions for evaporating portions of the a-Si layer without damaging the transparent electrodes. If the lower layer of each transparent electrode (under the step) is removed together with each portion of the a-Si layer forming a series connection will not then be possible because the edge of the transparent electrode will be covered.
A similar problem, as described above, will arise when a metal electrode, deposited on the patterned a-Si layer, is itself patterned. At any rate, it is difficult to perform the patterning accurately in such a structure so that the lower layer has a thickness step affecting the film thickness of the upper thin layer, as shown in FIG. 2. This is best accomplished by other patterning techniques other than laser patterning.